In an eye drop, a thermally unstable medicament, for example, a prostaglandin derivative such as latanoprost, isopropyl unoprostone, tafluprost or travoprost, an esterified steroid such as methylprednisolone sodium succinate or prednisolone acetate, a carboxylic acid ester such as ethyl parahydroxybenzoate, ethyl aminobenzoate, procaine or aspirin, or the like is sometimes added.
However, the storage temperature for an eye drop may sometimes increase during distribution or storage. In the case where a thermally unstable medicament is contained in an eye drop, when the medicament is degraded due to a rise of the storage temperature, a desired drug efficacy is not exhibited, and further, sometimes suspended matter may occur or the eye drop may become turbid. If it is stored in a cold place, the degradation of a thermally unstable medicament can be effectively prevented. However, an eye drop can be exposed to various environments, therefore, it is necessary to prevent the degradation of the medicament by a method other than the storage in a cold place.
On the other hand, it is general that a water-soluble organic amine is added to an eye drop as a buffer, however, the water-soluble organic amine is sometimes added for other purposes.
JP-A-2003-146881 discloses an invention relating to an anti-allergic ophthalmic preparation and describes that by adding an organic amine to an ophthalmic preparation containing pemirolast potassium (medicament), deposition of crystals of pemirolast potassium can be prevented. Further, JP-A-2003-327530 discloses an invention relating to an eye drop containing a tetrazole derivative and describes that by adding a basic amine compound, the preservative effect of a cationic preservative can be enhanced.
However, there is no report that by adding an organic amine to an eye drop containing a thermally unstable medicament, the medicament is stabilized thereby to prevent its degradation.